I've only owned peas for a couple years, but as I understand it, it's not possible to definitively sex whites until 2-3 years old when the males begin to grow their trains, except for of course a DNA test.

When the white pea gets 12 month, the male begin to have the train, not like the adult ones, but that's enough for you to tell the males from the females. The little ones are difficult, I try to find some differences.

How do your guys sex 3-5 months old white peachicks? I want to buy 2 male white peas, but I am unable to sex them, they seem similar

I know that this isn't the best advice but seeing the two on the right of the photo you can see one with long tail feathers and one has short tail feathers which could just be age difference or new feathers coming in if it the chicks are the same sex. Another thing that I don't know if it does work for sure is hens have wider, shorter wings and males have long, thin wings. Just some I've heard. 3 ways to sex Whites that I know that work without the need of DNA sexing. Neck feather, shape the tail feathers make and tail coverts or premature train. I don't have pictures to show the neck feathers since my camera won't capture the detail of it. As for tail feather shape it's of different color peafowl.

See how the premature train webbing of the feather is wispy and not solid? That's an indication of a male. Also the premature train feathers can grow past the tail while tail coverts will never grow longer than the tail

See how it's wispy? This is a premature train feathers from my White male.

Male tail feathers are tear drop like and each feather hasn't a different length.

Hens have more circular and the tail feathers keep relatively the same length for the most part.